The present invention is related to a communication system comprising at least a first node and a second node, the first node and the second node comprising a gateway being connectable to a packet switched network for interconnecting said first and second node.
The present invention is also related to a node for use in such a communication system and to a communication method.
With the current Private Virtual Networking (PVN) solution in advanced PABXes such as the Philips SOPHO iS3000 series, a private virtual network is established using dial-on-demand connections through the public circuit switched telephone network. The connection is called virtual, because the actual connections between the nodes in the network reside in the public network and are only present when information needs to be exchanged between nodes. If there are no available (unused) connections between nodes participating in a call, a normal public network call is initiated, to establish a transparent channel through the public network. If required, several public network calls are made to establish sufficient resources across the public network.
Communication between two nodes requires exactly one signalling channel and zero or more user channels. The signalling channel is used to set up the actual end-to-end call and offer PBX facilities to the users across the entire (private virtual) network. The user channels are used to transport the user (voice) information.
With the advent of Internet telephony, companies have shown that it is possible to use a packet switched network such as the Internet, rather than the Public Switched Telephone Network (PSTN) to carry telephony traffic. Certain scenarios also show that carrying telephony traffic on the Internet can be much more cost-effective than using the PSTN. This is especially the case when the connection to the Internet is a local connection. Companies can save on their long distance and international calls when these are routed through the Internet, using a local connection to an Internet Service Provider (ISP). Several companies have already come up with products which enable the interconnection of PBXs to the Internet. These products, known as gateways, interface to PBXs on one side and to the Internet on the other side.
The gateway""s function is to encode, compress and package the voice information originating from the PBX into packets and transmit these packets on the Internet and vice versa. In addition to this, these gateways exchange control information across the Internet. The control information contains information to set up the actual end-to-end call. This is similar to the use of the signalling channel used in SOPHO iS3000 PVN (see above). It is also possible to use additional control flows between gateways. For example, gateways could monitor the presence and availability of one another.
As mentioned in the introduction, gateways interface PBXs to the public Internet. The connection to the Internet can be either via a leased line or a dial-up link. The choice is a matter of economics. In the case of a dial-up link, two situations can be considered. In the first case, the dial-up links are established for the duration of the office hours and are not present at any other time. In the second case, the dial-up links are set up on-demand whenever a connection is required between two nodes in the PVN. Again, the choice is a matter of economics. The first case is straightforward and relatively easy to implement: simply establish the connections when office hours begin and tear them down when office hours end. The second case, however, poses some technical challenges, which are explained below.
In the SOPHO iS3000 PVN solution it is easy to set up an on-demand connection to another node in the network because both nodes are connected to the PSTN. When two nodes are supposed to communicate through the Internet, using dial-up connections, then a problem arises when the dial-up connections are not (yet) present. Obviously, the originating node can initiate a dial-up connection to the Internet when a call needs to be made to another node, but how does the node to which that call is destined know that it has to establish a connection as well.
The object of the present invention is to provide a solution for the above mentioned problem.
To provide a solution to the above mentioned problem the transmission system according to the invention is characterized in that at least the first node is arranged for requesting via a dial up connection, the second node to connect to the packet switched network in orer to enable a connection between the first node and the second node via the packet switched network.
By requesting the second node via a dial up connection to connect to the packet switched network, and by subsequently completing the call via the packet switched network, an easy way of establishing calls is obtained. It is observed that the call needed to request the node to connect to the packet switched network can be very short. Consequently the costs of such a call is very low.
An embodiment of the invention is characterized in that the first node is arranged for including the request into a connection set up message, and in that the second node is arranged for extracting the request from the connection set up message without answering the call from the first node.
By transferring the request to connect to the packet switched network by means of a set up message, it is possible to transfer said information without a call being actually established. If the second node is arranged for extracting the request from the set up message without answering the call, no calling costs are incurred at all for transferring the request. The present invention will now be explained with reference to the drawing figures.